fs/timerfd.c

   1 /*
   2  *  fs/timerfd.c
   3  *
   4  *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   5  *
   6  *
   7  *  Thanks to Thomas Gleixner for code reviews and useful comments.
   8  *
   9  */
  10
  11 #include <linux/alarmtimer.h>
  12 #include <linux/file.h>
  13 #include <linux/poll.h>
  14 #include <linux/init.h>
  15 #include <linux/fs.h>
  16 #include <linux/sched.h>
  17 #include <linux/kernel.h>
  18 #include <linux/slab.h>
  19 #include <linux/list.h>
  20 #include <linux/spinlock.h>
  21 #include <linux/time.h>
  22 #include <linux/hrtimer.h>
  23 #include <linux/anon_inodes.h>
  24 #include <linux/timerfd.h>
  25 #include <linux/syscalls.h>
  26 #include <linux/compat.h>
  27 #include <linux/rcupdate.h>
  28
  29 struct timerfd_ctx {
  30         union {
  31                 struct hrtimer tmr;
  32                 struct alarm alarm;
  33         } t;
  34         ktime_t tintv;
  35         ktime_t moffs;
  36         wait_queue_head_t wqh;
  37         u64 ticks;
  38         int clockid;
  39         short unsigned expired;
  40         short unsigned settime_flags;   /* to show in fdinfo */
  41         struct rcu_head rcu;
  42         struct list_head clist;
  43         bool might_cancel;
  44 };
  45
  46 static LIST_HEAD(cancel_list);
  47 static DEFINE_SPINLOCK(cancel_lock);
  48
  49 static inline bool isalarm(struct timerfd_ctx *ctx)
  50 {
  51         return ctx->clockid == CLOCK_REALTIME_ALARM ||
  52                 ctx->clockid == CLOCK_BOOTTIME_ALARM;
  53 }
  54
  55 /*
  56  * This gets called when the timer event triggers. We set the "expired"
  57  * flag, but we do not re-arm the timer (in case it's necessary,
  58  * tintv.tv64 != 0) until the timer is accessed.
  59  */
  60 static void timerfd_triggered(struct timerfd_ctx *ctx)
  61 {
  62         unsigned long flags;
  63
  64         spin_lock_irqsave(&ctx->wqh.lock, flags);
  65         ctx->expired = 1;
  66         ctx->ticks++;
  67         wake_up_locked(&ctx->wqh);
  68         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  69 }
  70
  71 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
  72 {
  73         struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
  74                                                t.tmr);
  75         timerfd_triggered(ctx);
  76         return HRTIMER_NORESTART;
  77 }
  78
  79 static enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
  80         ktime_t now)
  81 {
  82         struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
  83                                                t.alarm);
  84         timerfd_triggered(ctx);
  85         return ALARMTIMER_NORESTART;
  86 }
  87
  88 /*
  89  * Called when the clock was set to cancel the timers in the cancel
  90  * list. This will wake up processes waiting on these timers. The
  91  * wake-up requires ctx->ticks to be non zero, therefore we increment
  92  * it before calling wake_up_locked().
  93  */
  94 void timerfd_clock_was_set(void)
  95 {
  96         ktime_t moffs = ktime_mono_to_real((ktime_t){ .tv64 = 0 });
  97         struct timerfd_ctx *ctx;
  98         unsigned long flags;
  99
 100         rcu_read_lock();
 101         list_for_each_entry_rcu(ctx, &cancel_list, clist) {
 102                 if (!ctx->might_cancel)
 103                         continue;
 104                 spin_lock_irqsave(&ctx->wqh.lock, flags);
 105                 if (ctx->moffs.tv64 != moffs.tv64) {
 106                         ctx->moffs.tv64 = KTIME_MAX;
 107                         ctx->ticks++;
 108                         wake_up_locked(&ctx->wqh);
 109                 }
 110                 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 111         }
 112         rcu_read_unlock();
 113 }
 114
 115 static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
 116 {
 117         if (ctx->might_cancel) {
 118                 ctx->might_cancel = false;
 119                 spin_lock(&cancel_lock);
 120                 list_del_rcu(&ctx->clist);
 121                 spin_unlock(&cancel_lock);
 122         }
 123 }
 124
 125 static bool timerfd_canceled(struct timerfd_ctx *ctx)
 126 {
 127         if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
 128                 return false;
 129         ctx->moffs = ktime_mono_to_real((ktime_t){ .tv64 = 0 });
 130         return true;
 131 }
 132
 133 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
 134 {
 135         if ((ctx->clockid == CLOCK_REALTIME ||
 136              ctx->clockid == CLOCK_REALTIME_ALARM) &&
 137             (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
 138                 if (!ctx->might_cancel) {
 139                         ctx->might_cancel = true;
 140                         spin_lock(&cancel_lock);
 141                         list_add_rcu(&ctx->clist, &cancel_list);
 142                         spin_unlock(&cancel_lock);
 143                 }
 144         } else if (ctx->might_cancel) {
 145                 timerfd_remove_cancel(ctx);
 146         }
 147 }
 148
 149 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
 150 {
 151         ktime_t remaining;
 152
 153         if (isalarm(ctx))
 154                 remaining = alarm_expires_remaining(&ctx->t.alarm);
 155         else
 156                 remaining = hrtimer_expires_remaining(&ctx->t.tmr);
 157
 158         return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
 159 }
 160
 161 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
 162                          const struct itimerspec *ktmr)
 163 {
 164         enum hrtimer_mode htmode;
 165         ktime_t texp;
 166         int clockid = ctx->clockid;
 167
 168         htmode = (flags & TFD_TIMER_ABSTIME) ?
 169                 HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
 170
 171         texp = timespec_to_ktime(ktmr->it_value);
 172         ctx->expired = 0;
 173         ctx->ticks = 0;
 174         ctx->tintv = timespec_to_ktime(ktmr->it_interval);
 175
 176         if (isalarm(ctx)) {
 177                 alarm_init(&ctx->t.alarm,
 178                            ctx->clockid == CLOCK_REALTIME_ALARM ?
 179                            ALARM_REALTIME : ALARM_BOOTTIME,
 180                            timerfd_alarmproc);
 181         } else {
 182                 hrtimer_init(&ctx->t.tmr, clockid, htmode);
 183                 hrtimer_set_expires(&ctx->t.tmr, texp);
 184                 ctx->t.tmr.function = timerfd_tmrproc;
 185         }
 186
 187         if (texp.tv64 != 0) {
 188                 if (isalarm(ctx)) {
 189                         if (flags & TFD_TIMER_ABSTIME)
 190                                 alarm_start(&ctx->t.alarm, texp);
 191                         else
 192                                 alarm_start_relative(&ctx->t.alarm, texp);
 193                 } else {
 194                         hrtimer_start(&ctx->t.tmr, texp, htmode);
 195                 }
 196
 197                 if (timerfd_canceled(ctx))
 198                         return -ECANCELED;
 199         }
 200
 201         ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
 202         return 0;
 203 }
 204
 205 static int timerfd_release(struct inode *inode, struct file *file)
 206 {
 207         struct timerfd_ctx *ctx = file->private_data;
 208
 209         timerfd_remove_cancel(ctx);
 210
 211         if (isalarm(ctx))
 212                 alarm_cancel(&ctx->t.alarm);
 213         else
 214                 hrtimer_cancel(&ctx->t.tmr);
 215         kfree_rcu(ctx, rcu);
 216         return 0;
 217 }
 218
 219 static unsigned int timerfd_poll(struct file *file, poll_table *wait)
 220 {
 221         struct timerfd_ctx *ctx = file->private_data;
 222         unsigned int events = 0;
 223         unsigned long flags;
 224
 225         poll_wait(file, &ctx->wqh, wait);
 226
 227         spin_lock_irqsave(&ctx->wqh.lock, flags);
 228         if (ctx->ticks)
 229                 events |= POLLIN;
 230         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 231
 232         return events;
 233 }
 234
 235 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
 236                             loff_t *ppos)
 237 {
 238         struct timerfd_ctx *ctx = file->private_data;
 239         ssize_t res;
 240         u64 ticks = 0;
 241
 242         if (count < sizeof(ticks))
 243                 return -EINVAL;
 244         spin_lock_irq(&ctx->wqh.lock);
 245         if (file->f_flags & O_NONBLOCK)
 246                 res = -EAGAIN;
 247         else
 248                 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
 249
 250         /*
 251          * If clock has changed, we do not care about the
 252          * ticks and we do not rearm the timer. Userspace must
 253          * reevaluate anyway.
 254          */
 255         if (timerfd_canceled(ctx)) {
 256                 ctx->ticks = 0;
 257                 ctx->expired = 0;
 258                 res = -ECANCELED;
 259         }
 260
 261         if (ctx->ticks) {
 262                 ticks = ctx->ticks;
 263
 264                 if (ctx->expired && ctx->tintv.tv64) {
 265                         /*
 266                          * If tintv.tv64 != 0, this is a periodic timer that
 267                          * needs to be re-armed. We avoid doing it in the timer
 268                          * callback to avoid DoS attacks specifying a very
 269                          * short timer period.
 270                          */
 271                         if (isalarm(ctx)) {
 272                                 ticks += alarm_forward_now(
 273                                         &ctx->t.alarm, ctx->tintv) - 1;
 274                                 alarm_restart(&ctx->t.alarm);
 275                         } else {
 276                                 ticks += hrtimer_forward_now(&ctx->t.tmr,
 277                                                              ctx->tintv) - 1;
 278                                 hrtimer_restart(&ctx->t.tmr);
 279                         }
 280                 }
 281                 ctx->expired = 0;
 282                 ctx->ticks = 0;
 283         }
 284         spin_unlock_irq(&ctx->wqh.lock);
 285         if (ticks)
 286                 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
 287         return res;
 288 }
 289
 290 #ifdef CONFIG_PROC_FS
 291 static int timerfd_show(struct seq_file *m, struct file *file)
 292 {
 293         struct timerfd_ctx *ctx = file->private_data;
 294         struct itimerspec t;
 295
 296         spin_lock_irq(&ctx->wqh.lock);
 297         t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 298         t.it_interval = ktime_to_timespec(ctx->tintv);
 299         spin_unlock_irq(&ctx->wqh.lock);
 300
 301         return seq_printf(m,
 302                           "clockid: %d\n"
 303                           "ticks: %llu\n"
 304                           "settime flags: 0%o\n"
 305                           "it_value: (%llu, %llu)\n"
 306                           "it_interval: (%llu, %llu)\n",
 307                           ctx->clockid, (unsigned long long)ctx->ticks,
 308                           ctx->settime_flags,
 309                           (unsigned long long)t.it_value.tv_sec,
 310                           (unsigned long long)t.it_value.tv_nsec,
 311                           (unsigned long long)t.it_interval.tv_sec,
 312                           (unsigned long long)t.it_interval.tv_nsec);
 313 }
 314 #else
 315 #define timerfd_show NULL
 316 #endif
 317
 318 #ifdef CONFIG_CHECKPOINT_RESTORE
 319 static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 320 {
 321         struct timerfd_ctx *ctx = file->private_data;
 322         int ret = 0;
 323
 324         switch (cmd) {
 325         case TFD_IOC_SET_TICKS: {
 326                 u64 ticks;
 327
 328                 if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
 329                         return -EFAULT;
 330                 if (!ticks)
 331                         return -EINVAL;
 332
 333                 spin_lock_irq(&ctx->wqh.lock);
 334                 if (!timerfd_canceled(ctx)) {
 335                         ctx->ticks = ticks;
 336                         if (ticks)
 337                                 wake_up_locked(&ctx->wqh);
 338                 } else
 339                         ret = -ECANCELED;
 340                 spin_unlock_irq(&ctx->wqh.lock);
 341                 break;
 342         }
 343         default:
 344                 ret = -ENOTTY;
 345                 break;
 346         }
 347
 348         return ret;
 349 }
 350 #else
 351 #define timerfd_ioctl NULL
 352 #endif
 353
 354 static const struct file_operations timerfd_fops = {
 355         .release        = timerfd_release,
 356         .poll           = timerfd_poll,
 357         .read           = timerfd_read,
 358         .llseek         = noop_llseek,
 359         .show_fdinfo    = timerfd_show,
 360         .unlocked_ioctl = timerfd_ioctl,
 361 };
 362
 363 static int timerfd_fget(int fd, struct fd *p)
 364 {
 365         struct fd f = fdget(fd);
 366         if (!f.file)
 367                 return -EBADF;
 368         if (f.file->f_op != &timerfd_fops) {
 369                 fdput(f);
 370                 return -EINVAL;
 371         }
 372         *p = f;
 373         return 0;
 374 }
 375
 376 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 377 {
 378         int ufd;
 379         struct timerfd_ctx *ctx;
 380
 381         /* Check the TFD_* constants for consistency.  */
 382         BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
 383         BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
 384
 385         if ((flags & ~TFD_CREATE_FLAGS) ||
 386             (clockid != CLOCK_MONOTONIC &&
 387              clockid != CLOCK_REALTIME &&
 388              clockid != CLOCK_REALTIME_ALARM &&
 389              clockid != CLOCK_BOOTTIME &&
 390              clockid != CLOCK_BOOTTIME_ALARM))
 391                 return -EINVAL;
 392
 393         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 394         if (!ctx)
 395                 return -ENOMEM;
 396
 397         init_waitqueue_head(&ctx->wqh);
 398         ctx->clockid = clockid;
 399
 400         if (isalarm(ctx))
 401                 alarm_init(&ctx->t.alarm,
 402                            ctx->clockid == CLOCK_REALTIME_ALARM ?
 403                            ALARM_REALTIME : ALARM_BOOTTIME,
 404                            timerfd_alarmproc);
 405         else
 406                 hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
 407
 408         ctx->moffs = ktime_mono_to_real((ktime_t){ .tv64 = 0 });
 409
 410         ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
 411                                O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
 412         if (ufd < 0)
 413                 kfree(ctx);
 414
 415         return ufd;
 416 }
 417
 418 static int do_timerfd_settime(int ufd, int flags,
 419                 const struct itimerspec *new,
 420                 struct itimerspec *old)
 421 {
 422         struct fd f;
 423         struct timerfd_ctx *ctx;
 424         int ret;
 425
 426         if ((flags & ~TFD_SETTIME_FLAGS) ||
 427             !timespec_valid(&new->it_value) ||
 428             !timespec_valid(&new->it_interval))
 429                 return -EINVAL;
 430
 431         ret = timerfd_fget(ufd, &f);
 432         if (ret)
 433                 return ret;
 434         ctx = f.file->private_data;
 435
 436         timerfd_setup_cancel(ctx, flags);
 437
 438         /*
 439          * We need to stop the existing timer before reprogramming
 440          * it to the new values.
 441          */
 442         for (;;) {
 443                 spin_lock_irq(&ctx->wqh.lock);
 444
 445                 if (isalarm(ctx)) {
 446                         if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
 447                                 break;
 448                 } else {
 449                         if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
 450                                 break;
 451                 }
 452                 spin_unlock_irq(&ctx->wqh.lock);
 453                 cpu_relax();
 454         }
 455
 456         /*
 457          * If the timer is expired and it's periodic, we need to advance it
 458          * because the caller may want to know the previous expiration time.
 459          * We do not update "ticks" and "expired" since the timer will be
 460          * re-programmed again in the following timerfd_setup() call.
 461          */
 462         if (ctx->expired && ctx->tintv.tv64) {
 463                 if (isalarm(ctx))
 464                         alarm_forward_now(&ctx->t.alarm, ctx->tintv);
 465                 else
 466                         hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
 467         }
 468
 469         old->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 470         old->it_interval = ktime_to_timespec(ctx->tintv);
 471
 472         /*
 473          * Re-program the timer to the new value ...
 474          */
 475         ret = timerfd_setup(ctx, flags, new);
 476
 477         spin_unlock_irq(&ctx->wqh.lock);
 478         fdput(f);
 479         return ret;
 480 }
 481
 482 static int do_timerfd_gettime(int ufd, struct itimerspec *t)
 483 {
 484         struct fd f;
 485         struct timerfd_ctx *ctx;
 486         int ret = timerfd_fget(ufd, &f);
 487         if (ret)
 488                 return ret;
 489         ctx = f.file->private_data;
 490
 491         spin_lock_irq(&ctx->wqh.lock);
 492         if (ctx->expired && ctx->tintv.tv64) {
 493                 ctx->expired = 0;
 494
 495                 if (isalarm(ctx)) {
 496                         ctx->ticks +=
 497                                 alarm_forward_now(
 498                                         &ctx->t.alarm, ctx->tintv) - 1;
 499                         alarm_restart(&ctx->t.alarm);
 500                 } else {
 501                         ctx->ticks +=
 502                                 hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
 503                                 - 1;
 504                         hrtimer_restart(&ctx->t.tmr);
 505                 }
 506         }
 507         t->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 508         t->it_interval = ktime_to_timespec(ctx->tintv);
 509         spin_unlock_irq(&ctx->wqh.lock);
 510         fdput(f);
 511         return 0;
 512 }
 513
 514 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 515                 const struct itimerspec __user *, utmr,
 516                 struct itimerspec __user *, otmr)
 517 {
 518         struct itimerspec new, old;
 519         int ret;
 520
 521         if (copy_from_user(&new, utmr, sizeof(new)))
 522                 return -EFAULT;
 523         ret = do_timerfd_settime(ufd, flags, &new, &old);
 524         if (ret)
 525                 return ret;
 526         if (otmr && copy_to_user(otmr, &old, sizeof(old)))
 527                 return -EFAULT;
 528
 529         return ret;
 530 }
 531
 532 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
 533 {
 534         struct itimerspec kotmr;
 535         int ret = do_timerfd_gettime(ufd, &kotmr);
 536         if (ret)
 537                 return ret;
 538         return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
 539 }
 540
 541 #ifdef CONFIG_COMPAT
 542 COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 543                 const struct compat_itimerspec __user *, utmr,
 544                 struct compat_itimerspec __user *, otmr)
 545 {
 546         struct itimerspec new, old;
 547         int ret;
 548
 549         if (get_compat_itimerspec(&new, utmr))
 550                 return -EFAULT;
 551         ret = do_timerfd_settime(ufd, flags, &new, &old);
 552         if (ret)
 553                 return ret;
 554         if (otmr && put_compat_itimerspec(otmr, &old))
 555                 return -EFAULT;
 556         return ret;
 557 }
 558
 559 COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
 560                 struct compat_itimerspec __user *, otmr)
 561 {
 562         struct itimerspec kotmr;
 563         int ret = do_timerfd_gettime(ufd, &kotmr);
 564         if (ret)
 565                 return ret;
 566         return put_compat_itimerspec(otmr, &kotmr) ? -EFAULT: 0;
 567 }
 568 #endif